1. Field of the Invention
The present invention relates to an explosively actuated tool for driving a fastener, such as a pin, into a substrate, for example of concrete or steel.
2. Description of the Prior Art
Explosively actuated tools for driving a fastener, such as a pin, into a hard substrate, such as of concrete or steel, are in common use and operate by detonation of an explosive charge. In most prior tools of this type, detonation of the charge drives a piston within a barrel of the tool and the piston, in turn, drives the fastener which is positioned within the forward end of the barrel prior to firing. Tools of this general type will typically have a pistol grip and the tool is actuated by operation of a trigger associated with the grip.
A version of the tool has been developed for driving fasteners into substrates remote from the operator, for example for driving a fastener into a ceiling while the operator is still standing on the floor beneath the ceiling or for driving a fastener into a remote wall. This version of the tool is designed to be mounted at one end of a long handle or pole held by the operator. This version of the tool is termed a “pole tool”. Pole tools are disclosed in U.S. Pat. No. 5,465,893 and European patent application 1 197 301 (AU 6997/01). In these previously proposed pole tools, the barrel, which contains the fastener driving piston, is slidably mounted within the housing of the tool. The barrel is biased to a forwards position and when the forward end of the barrel is pressed against the substrate the barrel is caused to retract into the housing so that a charge chamber formed at the rear end of the barrel moves over and encloses the explosive charge. This occurs by the operator manipulating the pole so as to press the forward end of the barrel against the substrate. The pole itself is mounted to a firing pin mechanism of the tool and further pressing movement applied to the tool via the pole loads the firing pin mechanism which, when a predetermined loading is reached, releases the firing pin to detonate the charge.
With these previously proposed pole tools it is possible to fire the tool by holding the housing of the tool with one hand and pressing the pole inwardly with the other hand in order to load and then release the firing mechanism, so-called “air firing” of the tool. Although the consequences of this are unlikely to be particularly serious as, if the tool is operated in this mode, the barrel will not have been displaced rearwardly so that its charge chamber encloses the charge and as a result the power output of the tool will be greatly diminished, nevertheless the fact that the tool is able to be fired in this mode does give rise to concern.